1. Field of the Invention
The present invention relates to an improvement of an apparatus for elimination of clogging caused by biofouling in water conduits such as condenser tubes of a power plant cooling system.
2. Description of the Prior Art
Sea water or river water is sucked by a pump and is passed through a pipe into a heat-exchanger to cool it and is discharged through a pipe.
In such a cooling water system, the deposition and the propagation of shellfish and algae on the walls of the pipes and the heat-exchanger cause a decrease in water feeding rate and heat transfer rate. It has been proposed to prevent such deposition and propagation of shellfish and algae by dosing chlorine or a chlorine type compound into the cooling water so as to impart the germicidal and algacidal effect of chlorine.
FIG. 1 shows one embodiment of the apparatus for elimination of biofouling. In FIG. 1, the reference numeral (1) designates a cooling water passage. The cooling water sucked by a pump (2) is fed to a feeding pipe (3) to cool a water-exchanger (4) and is discharged through a discharging pipe (5). Reference numeral (6) designates an apparatus for elimination of biofouling. A solution of a chlorine type oxidizing agent such as sodium hypochlorite or a chlorine-water prepared by absorbing chlorine which is stored in a tank (7), is fed by a fixed delivery pump (8) at a desired ratio through an inlet pipe (9) into the cooling water in the pipe (3). The deposition and the propagation of shellfish and algae on the wall of the water cooling system (1) are eliminated by the germicidal and algacidal effect of chlorine or the chlorine type compound.
An effective residual chlorine concentration in the cooling water in the apparatus for elimination of biofouling is controlled to be about 0.5 ppm. Chlorine reacts with impurities in the cooling water to be consumed. Therefore, in order to maintain 0.5 ppm of the effective residual chlorine concentration, it is usually necessary to feed a chlorine component at higher chlorine concentration such as higher than 1 ppm depending upon the impurity concentration in the cooling water.
In the apparatus for elimination of biofouling by the chlorine type compound, it is necessary to maintain about 0.5 ppm of the effective residual chlorine concentration in the cooling water. Therefore, the quantity of chlorine is so much as to cause expensive operation cost. Moreover, chlorine and chloride are discharged to the public water environment such as sea and river water. This may cause public pollution caused by forming toxic compounds from chlorine and organic compounds in the water. In order to prevent such public pollution, it is necessary to equip the system with a waste water treating apparatus, which causes high cost.
In order to overcome these disadvantages of the apparatus for elimination of biofouling, it has been proposed to provide an apparatus for elimination of trouble caused by biofouling in the cooling water system without causing public pollution by using a biocide other than the chlorine type compound. Ozone has a number of desirable characteristics as a biocide. For example, ozone is easily self-decomposed within a short time and does not cause any impurity to remain except oxygen by its decomposition.
The deposition and propagation of shell-fish and algae on the walls of the cooling water system can be eliminated by continuously feeding ozone to provide the effective residual ozone concentration of about 0.1 ppm. In order to maintain 0.1 ppm of the effective residual ozone concentration, it is necessary to feed ozone at a rate corresponding to the residual ozone and ozone consumed by the oxidation of impurities. The rate of ozone fed is several times that of the effective residual ozone concentration such as about 0.5 ppm. The latter apparatus for elimination of biofouling by the deposition and propagation of shellfish and algae on the walls of the cooling water system has the advantage of no public pollution. However, it is not economical to utilize it in an industrial operation because the cost of ozone is four times of the cost chlorine.